In the past, techniques of performing time synchronization between communication devices which are physically separated from each other have been proposed (see Patent Document 1). As an example of such techniques, there is a technique using a synchronization-processing packet (a synchronous packet). FIG. 10 is a diagram illustrating a configuration example of a time-synchronizing device 90 related to the technique. The time-synchronizing device 90 includes a synchronous packet-transceiving unit 901, a synchronization control unit 902, a clock oscillator 904, and a time-managing unit 905. The time-synchronizing device 90 records a time counted by the time-managing unit 905 with a predetermined degree of accuracy through the clock oscillator 904 installed in its own device. However, even when the time-synchronizing device 90 performs time synchronization with a master device once, the synchronization accuracy degrades with the lapse of time, leading to a deviation. For this reason, typically, the time-synchronizing device 90 periodically performs transmission and reception of synchronous packets with the master device to perform a synchronization process.